1. Field of the Invention
The present invention relates to devices for removing deposited dust particles from, and preventing charged particles from depositing on, surfaces, and in particular, to such devices that employ an array of transparent electrodes embedded within a transparent dielectric protective panel overcoated with a semiconducting film.
2. Brief Description of the Related Art
The efficiency of solar photovoltaic arrays may be greatly degraded by the deposition of dust particles, which reduce the amount of light entering the array. There are other devices that also require transparency to light for maximum efficiency, and which likewise suffer when dust deposits on them. These devices can include, without limitation, optical windows such as employed in video cameras, optical or infrared detectors, windshields for various types of vehicles including automobiles and aircraft, and the like. The problem of dust deposition can be particularly severe in dry, windy climates.
Various solutions to the problem of dust deposition on solar arrays have been proposed but none has been entirely satisfactory as described below. References mentioned in this background section are not admitted to be prior art with respect to the present invention.
U.S. Pat. No. 4,321,419 to Hanafin discloses a transparent protective cover for a solar panel. The cover includes a pair of rollers on opposite sides of the solar panel supporting a supply of film material. Clean film material is advanced over the solar panel to prevent excessive dust accumulation.
Electromagnetic traveling wave devices have been employed for moving and sorting particles. A detailed discussion of the theory and practice of using multi-phase traveling electromagnetic waves is presented in WO 0105514. A practical application of these principles is disclosed in U.S. Pat. No. 3,778,678 to Masuda. Masuda discloses a tubular duct of insulating material having three electrodes spirally wound along its outer surface. The electrodes are connected a three-phase current source to produce a traveling wave in the duct by which particles are propelled lengthwise along the duct.
Likewise, a toner-transporting apparatus is disclosed in U.S. Pat. No. 4,647,179 to Schmidlin. Schmidlin discloses a linear electrode array consisting of spaced apart electrodes to which a multi-phase alternating current (“AC”) voltage is connected. A traveling wave is formed thereby for transporting toner particles from a toner supply to an imaging surface.
However, to the knowledge of the present inventors such traveling wave techniques have not been applied to the problem of clearing dust particles from the surface of a solar photovoltaic array, an optical window, or similar types of devices where it is desirable to keep a surface free of obscuring dust and to provide maximum light transmission with minimal operational power requirements by employing transparent electrodes, an infrared reflecting film, and automatic (need-based) operation.
The limitations of the prior art are overcome by the present invention as described below.